diff --git a/bus/connection.c b/bus/connection.c
index add1c8b8..95bc6c0a 100644
--- a/bus/connection.c
+++ b/bus/connection.c
@@ -2374,6 +2374,21 @@ bus_transaction_send_from_driver (BusTransaction *transaction,
   if (!dbus_message_set_sender (message, DBUS_SERVICE_DBUS))
     return FALSE;
 
+  /* Make sure the message has a non-zero serial number, otherwise
+   * bus_transaction_capture_error_reply() will not be able to mock up
+   * a corresponding reply for it. Normally this would be delayed until
+   * the first time we actually send the message out from a
+   * connection, when the transaction is committed, but that's too late
+   * in this case.
+   */
+  if (dbus_message_get_serial (message) == 0)
+    {
+      dbus_uint32_t next_serial;
+
+      next_serial = _dbus_connection_get_next_client_serial (connection);
+      dbus_message_set_serial (message, next_serial);
+    }
+
   if (bus_connection_is_active (connection))
     {
       if (!dbus_message_set_destination (message,
diff --git a/dbus/dbus-connection-internal.h b/dbus/dbus-connection-internal.h
index d6947d18..df3c7010 100644
--- a/dbus/dbus-connection-internal.h
+++ b/dbus/dbus-connection-internal.h
@@ -55,6 +55,8 @@ DBUS_PRIVATE_EXPORT
 DBusConnection *  _dbus_connection_ref_unlocked                (DBusConnection     *connection);
 DBUS_PRIVATE_EXPORT
 void              _dbus_connection_unref_unlocked              (DBusConnection     *connection);
+DBUS_PRIVATE_EXPORT
+dbus_uint32_t     _dbus_connection_get_next_client_serial      (DBusConnection *connection);
 void              _dbus_connection_queue_received_message_link (DBusConnection     *connection,
                                                                 DBusList           *link);
 dbus_bool_t       _dbus_connection_has_messages_to_send_unlocked (DBusConnection     *connection);
diff --git a/dbus/dbus-connection.c b/dbus/dbus-connection.c
index a61e56a6..e6fedbbe 100644
--- a/dbus/dbus-connection.c
+++ b/dbus/dbus-connection.c
@@ -1459,7 +1459,16 @@ _dbus_connection_unref_unlocked (DBusConnection *connection)
     _dbus_connection_last_unref (connection);
 }
 
-static dbus_uint32_t
+/**
+ * Allocate and return the next non-zero serial number for outgoing messages.
+ *
+ * This method is only valid to call from single-threaded code, such as
+ * the dbus-daemon, or with the connection lock held.
+ *
+ * @param connection the connection
+ * @returns A suitable serial number for the next message to be sent on the connection.
+ */
+dbus_uint32_t
 _dbus_connection_get_next_client_serial (DBusConnection *connection)
 {
   dbus_uint32_t serial;